1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus for real time display of three dimensional information of a diagnosed portion of an object
2. Discussion of the Background
In general, in the conventional ultrasonic diagnostic system, a predetermined cross sectional surface is scanned by an ultrasonic beam transmitted from an ultrasonic probe in the form of a one dimensional array of piezoelectric transducers and a cross sectional image based on two dimensional information is displayed. On the other hand, experiments have been performed to obtain three dimensional picture image information (i.e., volume image) by operating the ultrasonic probe in a three dimensional space. In an ultrasonic diagnostic apparatus, the display of three dimensional image has been expected to develop a new approach to diagnosis. Research has proceeded to changing a direction of an ultrasonic beam by manually or mechanically moving a convex probe and a linear array probe for an abdominal region, and using a multi plane probe having a mechanism for rotating an electronic sector for an oesophagus region.
In such a three dimensional ultrasonic diagnostic apparatus, three dimensional scanning in order to obtain three dimensional information is very time consuming compared to cross sectional scanning in a conventional two dimensional ultrasonic diagnostic apparatus. In the case of detecting an object exhibiting quick movement, such as a heart, scanning can not follow such a quick movement. A display of such an object is sometimes distorted. In the case of an object exhibiting slow movement, such as an abdominal region using a fixed probe is insufficient, yet if a moving probe is used, and the moving speed of the probe is not constant, the display of the abdominal region is greatly distorted.
Therefore, an ultrasonic diagnostic apparatus has been developed including a two dimensional probe having an electronic scanning two dimensional phased array of piezoelectric transducers and an ultrasonic probe having a function of electronically scanning three dimensional space with a ultrasonic beam so that a three dimensional volume image is scanned at a frame rate nearly 30 frame/second (real time).
The three dimensional volume image provides information along a front-rear direction which can not be obtained in a conventional two dimensional cross sectional image and provides a capability to observe a diagnosed portion at any point of sight. However, in so doing, it is necessary to change and rotate an observed cross sectional surface. Such a capability makes it easy to reproduce a picture image at one moment and to reproduce an animation image repeatedly at several seconds. However, in the case of diagnosing an object using a continuous animation image such as an ultrasonic diagnostic image, it is again difficult to process the entire three dimensional image information due to limitations on processing speed. However, an operation of changing and rotating an observed cross sectional surface is not necessary for the entire three dimensional image.
In an ultrasonic diagnostic apparatus for scanning/displaying a three dimensional volume image at real time, a request to observe an image at a frame rate substantially equal to that of a conventional two dimensional cross sectional image at a cross sectional surface would be considered in the case of displaying a three dimensional volume image. In the case of always three dimensionally scanning and reconstructing a two dimensional cross sectional image based on a received three dimensional information, a resolution level of three dimensional information is not considered of great importance in order to maintain a frame rate at real time. Therefore, an amount of ultrasonic energy for three dimensionally scanning is more than that for a conventional two dimensional ultrasonic diagnostic apparatus which obtains two dimensional image information of the same quality as that of the conventional two dimensional ultrasonic diagnostic apparatus. This presents a safety problem.
As described above, a conventional three dimensional ultrasonic diagnostic apparatus has a drawback of not displaying the entire three dimensional information in real time and a drawback of needing more ultrasonic energy than that of a conventional apparatus in order to display a two dimensional cross sectional image.